BRAKE SYSTEM
Brakes 1986 MERCEDES-BENZ
DESCRIPTION
Service brake system utilizes 4-wheel disc brakes, hydraulically-operated by a tandem or stepped tandem master cylinder and power brake unit. Stop screw is on top center of stepped tandem master cylinder and bottom center of tandem master cylinder.
Master cylinders manufactured by ATE, Bendix and Girling utilize 2 or 3-chamber reservoirs. A fluid level sensor contact is built into each chamber. A dash panel warning light is activated when brake fluid level is low or when pressure differential between two brake circuits is caused by loss of fluid in one circuit.
Floating type front disc brake calipers are used on the 190, 420 and 560 series; fixed calipers on other models. Parking brakes are cable-actuated and housed in rear brake rotors. All models have brake pad wear indicator and differential pressure warning indicator. Wear indicator for 420 and 560 series operates on inner pads only.
The Anti-Lock Brake System (ABS) is standard on 420SEL, 300 and 560 series (optional on 190 series). See Mercedes-Benz ANTI-LOCK BRAKE SYSTEM (ABS) article. On diesel models, a vacuum pump is incorporated to supply a vacuum to the power brake unit.
ADJUSTMENTS
PEDAL HEIGHT & FREE PLAY
Pedal height, measured from pedal pad to pedal stop, should be 5.9" (150 mm). To adjust, loosen lock nuts and turn stop light switch until correct pedal height is obtained. Tighten lock nuts. Pedal free play should be .20-.60" (5-15 mm).
BRAKE LIGHT SWITCH
Stoplight switch is located under dash, above brake pedal. Loosen lock nuts and adjust switch so that contact button extends .24-.32" (6-8 mm). Tighten lock nuts.
PARKING BRAKE
1. Remove one wheel lug bolt at each rear wheel. Raise and support vehicle.
2. Rotate wheel until lug bolt hole is positioned over parking brake adjuster, approximately 45 degrees forward for diagonal swing axle and 90 degrees forward for diagonal swing axle with starting torque compensation. See Fig. 1 .
Fig. 1: Adjusting Parking Brake Mechanism
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
NOTE: Parking brake must be adjusted if brake pedal can be depressed by more than 2 steps (of 6) without any braking effect. DO NOT alter adjusting screw on parking brake intermediate lever. Screw is for balancing cable lengths only.
3. Using screwdriver inserted through lug bolt hole, hand turn adjuster until rear wheel cannot be turned. Back off adjuster until wheel can be turned without drag.
TESTING
BRAKE WARNING LIGHT
1. Dual warning light is mounted on dash. Turn ignition on. Light should glow when parking brake lever is pulled one notch and go off when lever is fully released.
2. To check circuit warning sensor, turn ignition on, release parking brake and ensure light is off. Open bleeder screw on one wheel and depress brake pedal. Light should glow.
3. Close bleeder screw, replenish brake fluid and bleed hydraulic system. Check that light goes out after testing. If not, differential pressure pin in master cylinder must be reset.
REMOVAL & INSTALLATION
DISC BRAKE PADS
Removal (420SEL, 300 & 560 Series)
1. Raise vehicle, support with safety stands and remove wheels. Remove upper hex head caliper bolt.
2. Pull clip of brake pad wear sensor out of plug by opening cap on plug. Rotate caliper downward and remove disc pads from carrier. If reuseable, note condition and location of pads for proper assembly.
3. Standard front disc brake pad assembly thickness, including lining backing plate, is .69" (17.5 mm). Standard rear pad assembly thickness is .61" (15.5 mm).
4. Front backing plate thickness is .18" (4.5 mm). Rear backing plate thickness is .20" (5 mm). Minimum pad thickness is .08" (2 mm).
NOTE: All self-locking, hex head bolts should only be used once.
Fig. 2: Mercedes-Benz Single Piston Disc Brake Caliper
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Installation
1. Using brass cylinder brush, clean disc pad guide surface in caliper. Siphon sufficient fluid from master cylinder reservoir to prevent overflowing. Press piston to bottom of bore.
2. Install disc pads and wear sensor wires. Reverse removal procedure to complete installation. Check that dash light goes out. Reset pin in master cylinder, if necessary.
Removal (All Other Models)
1. Raise vehicle, support with safety stands and remove wheels. Remove cover plate from caliper and disconnect wear indicator wires (if equipped).
2. Drive out retaining pins toward inside of vehicle. On Bendix brakes, retaining pins have locking keys. Remove cross spring.
3. Remove disc pads from caliper assembly. If reusable, note condition and location of pads for proper assembly.
4. Standard front disc brake pad assembly thickness, including lining backing plate, is .69" (17.5 mm). Standard rear pad assembly thickness is .59" (15 mm).
5. Front backing plate thickness is .18" (4.5 mm). Rear backing plate thickness is .20" (5 mm). Minimum pad thickness is .08" (2 mm).
NOTE: All self-locking, hex head bolts should only be used once.
Installation
1. Using cylinder brush, clean disc pad guide surface in caliper. Siphon sufficient fluid from master cylinder reservoir to prevent overflowing. Press pistons to bottom of bores.
2. Apply Molykote to back of disc brake pads. See Fig. 3 . Install disc pads, cross spring and retaining pins.
Fig. 3: Mercedes-Benz Disc Brake Pad
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
3. Install cover plate, retaining pin locking keys and wear sensor wires (if equipped). Check that dash light goes out. Reset pin at master cylinder, if necessary.
DISC BRAKE CALIPER
Removal
1. Raise and support vehicle. Remove wheel and tire. Open bleeder screw on caliper assembly and pump out fluid. Disconnect and plug brake lines at caliper assembly.
2. Remove caliper attaching bolts. Remove caliper assembly from vehicle.
Installation
To install, reverse removal procedure. Replace hex head mounting bolts when installing caliper. Tighten all nuts and bolts, bleed hydraulic system and check that dash light goes out. Reset pin in master cylinder, if necessary.
DISC BRAKE ROTOR
Removal (Front)
1. Remove caliper assembly and hub grease cap. Remove contact spring for radio shielding. Loosen clamping nut socket screw on wheel spindle.
2. Remove clamping nut and washer. Remove wheel hub and rotor assembly. Remove bolts securing hub to rotor. Remove rotor.
Cleaning & Inspection
1. Clean rotor and check for cracks, scoring or excessive wear. Replace as necessary.
2. Before installing stock replacement rotor, use solvent to remove nitrocellulose corrosion preventive paint from rotor surface.
Installation
To install, reverse removal procedure. Tighten all bolts and fittings evenly. Bleed hydraulic system, if necessary. Lubricate and adjust wheel bearings. See appropriate article in SUSPENSION section.
Removal (Rear)
1. Raise and support vehicle. Remove rear wheel and tire. Disconnect and plug brake lines. Remove caliper assembly.
2. Using rear axle shaft Assembly Tool (116 589 24 61 00), pull rotor out from axle shaft flange. See Fig. 4 .
Fig. 4: Assembled View of Rear Rotor & Caliper
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Installation
1. To install, reverse removal procedure. Coat axle splines with high-temperature lubricant. Grease wheel bearings, seal as necessary and install.
2. Tighten all bolts and fittings evenly. Bleed hydraulic system, if necessary.
REAR AXLE SEAL
Removal
1. Raise and support vehicle. Remove rear wheel and tire. Release locking plates. Remove mount bolts and caliper. Wire caliper out of the way.
2. On vehicles with starting torque compensation, disconnect brake hose holder and hang caliper assembly with wire.
3. Loosen and remove 8 mm bolt or 12 mm bolt with spacing sleeve and clamping disc at center of rear brake rotor.
4. Using rear axle shaft Assembly Tool (116 589 24 61 00) or equivalent, remove rotor from rear axle shaft flange. Pry rear axle seal from rotor at inner wheel bearing and discard.
NOTE: If brake rotor is difficult to free from axle flange, strike outer circumference lightly with plastic hammer. Ensure parking brake is released.
Installation
1. Coat inside of new axle seal lip and wheel bearings with grease. Install bearings and seal into rear brake rotor.
2. Coat axle splines with heat resistant lubricant and install rotor. To complete installation, reverse removal procedure.
MASTER CYLINDER
Removal
1. Drain master cylinder brake fluid. Disconnect and plug brake lines. Disconnect electrical wires.
2. Remove bolts securing master cylinder to power brake unit. Remove master cylinder.
Installation
1. Reverse removal procedure. Always replace rubber "O" ring seal between master cylinder and power unit.
2. Bleed hydraulic system and check complete system for fluid leaks. Check that dash light is out and reset pin in master cylinder, (if necessary).
PARKING BRAKE LININGS
Removal
1. Raise and support vehicle. Remove wheel and tire. Disconnect hydraulic line. Remove caliper and rotor. Turn rear axle flange until one threaded hole faces hold-down spring. Compress spring with Spring Installer Tool (040) and turn 90 degrees.
2. Remove all retainers and hold-down springs. Detach lower return spring, opposite adjuster. Pull brake shoes apart, enough to remove over rear axle shaft flange. Detach upper return spring. Remove adjuster.
Cleaning & Inspection
Use brake vacuum cleaner to clear asbestos dust from assembly and check condition of linings and components.
NOTE: Disc brake rotor inside diameter is 6.30" (160 mm). Parking brake lining width is .98" (25 mm).
Installation
1. To install, reverse removal procedure. Lubricate all adjuster components and sliding surfaces of backing plate with silicone brake grease.
2. Return adjuster to home position. Install on shoes with adjusting wheel facing 45 degrees forward (diagonal swing axle) or 90 degrees forward (diagonal swing axle with starting torque compensation).
3. Attach hold-down springs, retainers and return springs. Install rotor and adjust parking brake.
SINGLE DIAPHRAGM & PISTON TYPE VACUUM PUMP
Removal (Diesel Only)
While holding lock nut(s), loosen vacuum line(s) from pump. Detach hex head mount screws from crankcase and remove vacuum pump and gasket.
NOTE: Piston type vacuum pump screw connector is provided with oil retention valve. When pump is stopped and vacuum is available, valve prevents engine oil from entering power brake unit.
Installation
Install vacuum pump with new gasket to crankcase. New gasket thickness is .0078" (.2 mm). Connect vacuum lines and test for proper operation.
DOUBLE DIAPHRAGM VACUUM PUMP
Removal (Diesel Only)
1. Loosen upper radiator hose and drain some coolant. Remove fan, radiator shell and power steering pump "V" belt.
2. Loosen vacuum lines from pump. Remove hex head mount screws from crankcase. Remove vacuum pump with toothed intermediate sleeve and gasket.
Installation
1. Clean sealing surfaces and install pump with new gasket to crankcase. Ensure intermediate sleeve and pump locating pins are properly seated in crankcase.
2. Connect vacuum lines to pump. Install "V" belt, radiator shell, fan and hose. Check pump for proper operation.
OVERHAUL
FRONT DISC BRAKE CALIPERS
Disassembly (420SEL, 300 & 560 Series)
Remove caliper from vehicle. Place piece of wood in front of piston. Gradually apply compressed air to fluid inlet. Remove piston. Remove dust boot from piston and piston seal from caliper bore.
Cleaning & Inspection
1. Wash parts in denatured alcohol or brake fluid and air dry. Inspect caliper bore and piston for scoring, scratches or rust. Standard front brake caliper bore inside diameter is 2.36" (60 mm).
2. Replace dust boot and piston seal when disassembling caliper. Remove small rust deposits in bore with fine emery cloth.
CAUTION: When installing new caliper, check that calipers on same axle have pistons of same diameter. Only identical calipers should be installed on front axle.
Reassembly
Coat piston and caliper bore with ATE brake cylinder paste. Install piston seal into caliper bore. Install piston and dust boot.
Disassembly (190, 300E, 300SDL & 420SEL)
NOTE: This procedure also applies to all rear calipers.
1. Remove caliper from vehicle. Remove disc pads from caliper and remove dust boot.
2. Hold one piston in place using piston Resetting Pliers (123 589 00 37 00). Gradually apply compressed air to fluid inlet to remove opposite piston. See Fig. 5 .
Fig. 5: Disassembled View of Dual Piston Brake Caliper
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
3. Remove piston seal from groove of cylinder bore. Remove remaining piston and seal in same manner.
NOTE: DO NOT separate caliper halves. Replace only as an assembly. Calipers installed on front axle must be from same manufacturer. Calipers on rear axle may be different only if same brand replacement part is unavailable.
Cleaning & Inspection
1. Check cylinder bores of caliper for wear or damage. Small rust deposits may be removed from caliper bores with polishing cloth.
CAUTION: DO NOT clean chrome-plated surfaces of pistons with polishing or emery cloth. Damage to surface may result. Remove deposits with soft brass wire brush or rough cleaning cloth. Replace piston, if chrome surface is damaged.
2. Heavy rust deposits or badly scored bore will require replacement of caliper. Rust deposits in front of piston seal groove may be removed with fine emery cloth.
3. Standard front brake caliper bore inside diameter is 2.36" (60 mm). Standard rear caliper bore I.D. (Teves) is 1.49" (38 mm) and rear caliper bore I.D. (Bendix/Girling) is 1.65" (42 mm).
Reassembly
1. Coat piston and caliper bore with ATE brake cylinder paste. Install piston seal into caliper bore and install piston.
NOTE: With caliper installed on diagonal swing axle, elevation on piston faces upward. On diagonal swing axle with starting torque compensation, elevation on piston must be at bottom and project at least .004" (.10 mm) above shield. Use DOT 4 or higher rated brake fluid during overhaul.
2. Check position of piston in caliper with Piston Gauge (000 589 34 23 00 for front or 000 589 35 23 00 for rear).
3. Adjust with Piston Rotating Pliers (000 589 50 37 00). Install dust boot. Install heat shield into piston, with recess in shield fitting into elevation of piston.
REAR DISC BRAKE CALIPER
Overhaul procedure is the same as front caliper of 300E, 300SDL and 420SEL models.
MASTER CYLINDER
CAUTION: Bendix master cylinder (painted Blue) cannot be overhauled. Replace as an assembly only.
Disassembly (Tandem & Stepped Tandem)
1. On tandem master cylinder, remove reservoir and push piston in. Remove stop screw. Remove push rod piston assembly and "O" ring.
2. Remove lock ring from housing. Remove floating circuit piston, stop washer, 2 vacuum seals and intermediate ring.
3. Tap lightly on housing with plastic mallet to remove floating circuit piston assembly. See Fig. 6 .
NOTE: On Teves reservoir only, remove cap, end covers, strainer, splash guard, "O" rings and contact inserts. On Bendix model, remove strainer from cover. DO NOT remove contact inserts. Always use DOT 4 or higher rated brake fluid during overhaul.
Fig. 6: Sectional View of Tandem Master Cylinder
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Cleaning & Inspection
1. Clean all parts with denatured alcohol or brake fluid and flush residue out of housing. Check bore in housing and piston for score marks and rust.
2. Small rust spots in housing may be removed with polishing cloth. Scored or badly rusted parts cannot be repaired and require replacement of complete master cylinder.
3. On tandem models, standard master cylinder inside diameter is .937" (23.81 mm). Maximum bore wear limit is .941" (23.92 mm).
4. On stepped tandem models, standard master cylinder I.D. for push rod circuit is .937" (23.81) and I.D. for floating circuit is .750" (19.05 mm).
5. Maximum master cylinder bore I.D. is .941" (23.92 mm) for push rod circuit and .754" (19.16 mm) for floating circuit.
Reassembly
1. To assemble, reverse disassembly procedure. Coat bore of master cylinder with brake fluid.
2. Install new floating circuit piston assembly. Push in piston assembly and install lock ring.
3. Install new push rod piston assembly. Screw in stopper screw using new copper washer for Gray iron master cylinder or new aluminum washer for light alloy master cylinder.
4. Replace "O" ring to ensure proper vacuum seal at power brake unit. Bleed hydraulic system. Check that dash light is out.
NOTE: Differential pressure warning indicator reset pin, located at front end of master cylinder, MUST be reset once indicator light in dash panel has been triggered.
POWER BRAKE UNIT
Manufacturer does not recommend disassembly of this unit. If problem is found in power brake unit, complete assembly must be replaced. DO NOT disassemble power brake unit.
NOTE: Determine whether source of problem is in power brake unit or check valve. Inspect check valve first.
TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS
Application Ft. Lbs. (N.m)
Brake Pressure
Switch-to-Master Cylinder 11-22 (15-30)
Caliper Mounting Bolts
Front
190 & 300 Series 83 (113)
420 & 500 Series 26 (35)
Rear (All Models) 67 (90)
Hub-to-Rotor Bolts 83 (113)
DISC BRAKE SPECIFICATIONS
DISC BRAKE ROTOR SPECIFICATIONS
Application Specification
190, 300
(Front)
Disc. Diameter In. (mm)
Standard 10.31 (262)
Heavy Duty 10.95 (278)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm)
Standard .433 (11.0)
Heavy Duty .866 (22.0)
Min. Refinish Thickness In. (mm)
Standard .354 (9.0)
Heavy Duty .787 (20.0)
Min. Refinish Thickness In. (mm)
Standard .354 (9.0)
Heavy Duty .787 (20.0)
(Rear)
Disc. Diameter In. (mm) 10.95 (278)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm) .394 (10.0)
Min. Refinish Thickness In. (mm) .327 (8.3)
Discard Thickness In. (mm) .327 (8.3)
420 SEL
(Front)
Disc. Diameter In. (mm) 11.25 (286)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm) .866 (22.0)
Min. Refinish Thickness In. (mm) .76 (19.4)
Discard Thickness In. (mm) .76 (19.4)
(Rear)
Disc. Diameter In. (mm) 11.0 (279)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm) .394 (10.0)
Min. Refinish Thickness In. (mm) .327 (8.3)
Discard Thickness In. (mm) .327 (8.3)
560 SEL
(Front)
Disc. Diameter In. (mm) 10.95 (278)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm) .866 (22.0)
Min. Refinish Thickness In. (mm) .76 (19.4)
Discard Thickness In. (mm) .76 (19.4)
(Rear)
Disc. Diameter In. (mm) 11.0 (279)
Lateral Runout In. (mm) .005 (.12)
Parallelism In. (mm) .0008 (.02)
Original Thickness In. (mm) .394 (10.0)
Min. Refinish Thickness In. (mm) .327 (8.3)
Discard Thickness In. (mm) .327 (8.3)